1. Field of the Invention
The present invention relates to a magenta inkjet ink composition, and more particularly to a magenta inkjet ink composition with good pH value stability.
2. Description of the Related Art
In recent years, the dye added to color inkjet ink is generally maintained within a range from neutral to weakly basic. An ink which is too acidic or too basic erodes the print head and reduces the dyeability of the print medium (such as paper), thus print quality suffers. Ink stored or operated at high temperature degrades rapidly, further affecting print quality. The adverse phenomenon is more apparent when reactive dye is used.
In color inkjet printing, a primary dye set includes cyan ink, magenta ink, yellow ink, and black ink. In order to obtain good color and address the disadvantage of single colorant, any one of the four inks generally includes more than two colorants. For example, reactive dye RR31 can be used to adjust magenta color. The functional groups of the reactive dye, however, easily react with water resulting in decomposition thereof. Thus, the entire ink becomes acidic (that is, pH value decreases).
A small amount of a pH buffer solution is generally added to prevent hydrolysis of ink due to the reactive dye. For example, in U.S. Pat. No. 5,858,075, U.S. Pat. No. 6,176,913, and Japan. Pat. No. 2002241639, a pH buffer solution is added to the ink composition to prevent degradation (hydrolysis). Hydrolysis is a continuous reaction, however, and the buffer solution is consumed gradually. Therefore, the effectiveness of the buffer solution is reduced over time.